Triangles and Squares for a Unique Molecular Crystal Structure: Unsupported Two‐Coordinate Lithium Cations and CC Agostic Interactions in Cyclopropyllithium Derivatives

Abstract

Understanding and controlling the aggregation state is germane to alkyllithium chemistry. Lewis base-free alkyllithium compounds normally form tetrahedral tetramers or octahedral hexamers in the solid state with the lithium cations being three-coordinate. We report that the unsupported cyclopropyl derivative 1-(trimethylsilyl)cyclopropyllithium [{μ-c-C(SiMe )C H }Li] (1), synthesized by the reduction of 1-(phenylthio)-1-(trimethylsilyl)cyclopropane, crystallizes as a tetramer in the space group I-4 with the two-coordinate lithium atoms forming a square. CC agostic interactions complete the coordination sphere around each lithium. The aggregate is preserved in hydrocarbon solution. Furthermore, CC agostic interactions compete intra- and intermolecularly with Lewis base donation as in the unsaturated dimer of 1-(phenylthio)cyclopropyllithium [Li(thf) {μ-c-C(SPh)C H } Li (thf)] (3) which is also fully characterized.

Reactivity of Tantalum/Iridium and Hafnium/Iridium Alkyl Hydrides with Alkyl Lithium Reagents: Nucleophilic Addition, Alpha-H Abstraction, or Hydride Deprotonation?

“…In the solid-state structure, the Li cation interacts with the neopentylidene carbon (Li–C alkylidene distance = 2.25(4) Å) and points toward the hydrides of an adjacent complex (Ir···Li separation = 2.63(3) Å). The distance between the alkylidene carbon and the lithium center is compatible with a covalent bond. , …”

A New Phenanthroline Ligand and the Spontaneous Resolution of its Homoleptic Copper(I) Complex

“…[ 14 ] A reasonable hypothesis is based on the fact that aryl‐ or alkyllithium reagents are able to adopt many different polynuclear structures. [ 15 ] In our case, we can postulate the presence of a lithium cation (or two) within the chelating site of the phenanthroline after the addition of the first aryl group, together with other ligands (L n ) surrounding the cation(s) (see Figure 3). The formation of such an intermediate would preclude the second substitution at position 9 and orient the functionalization to position 7.…”

The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy

“…The Cs analogue, on the other hand, exhibited diffusion coefficients consistent with penta-or hexameric aggregates [206]. A range of s-block metal complexes, containing ligands such as hexamethyldisilazide [207], the bulky bis(4,6tbutylbenzoxazol-2-yl)methane [208], and 1 (trimethylsilyl) cyclopropyllithium [209] have all successfully been characterised by a combination of diffusion NMR and external calibration calculations.…”